This method can be used to identify rare or novel deleterious variants as genetic causes of disease and may be to the treatment implication like in the case described by Ellyard et al. The authors performed WES in a 4 year old girl with early onset SLE and discovered a rare, homozygous mutation in the three prime repair exonuclease 1 gene (TREX1) that was predicted to be highly deleterious. The gene discussed is TREX1; the disease is systemic lupus erythematosus.